In his recent state of the nation address, President Vladimir Putin said the most urgent problem facing Russia is its demographic crisis.

The country's population is declining by at least 700,000 people each year, leading to slow depopulation of the northern and eastern extremes of Russia, the emergence of hundreds of uninhabited "ghost villages" and an increasingly aged workforce.

Now, one of Russia's leading sociologists has warned that the country's population may halve by the
middle of this century.

Official Russian forecasts, along with those from international organisations like the UN, predict a decline from 146 million to between 80 and 100 million by 2050.

But in an exclusive interview to the BBC, Viktor Perevedentsev, who has been studying Russia's population since the 1960s, said he believed even these figures may be overly optimistic.

He said the decline was likely to accelerate and that the Russian leadership should accept the population had reached a "tipping point", beyond which direct intervention would be ineffective.

Birth-rates in many developed, industrialised countries are stagnant or declining. But when this is combined with very low life-expectancy and an increasingly unhealthy population, Mr Perevedentsev agrees that the term "catastrophe" reflects reality. It is not a case of hyperbole from overly emotional Russian patriots, he says.

Angry debate

Mr Perevedentsev explained that people have the majority of children between certain definable ages. In Russia, this is generally earlier than in Western countries. But the percentage of potential parents of child-bearing age within the Russian population is itself so small that state-funded efforts, by definition, can bring only temporary results.

The collapse of the Russian population, in my view, will not only continue, but it will actually accelerate

Viktor Perevedentsev

Mr Perevedentsev points to how the Soviet government, at the beginning of the 1980s, undertook similar measures in response to concerns over falling birth-rates. They produced a mini "baby boom", lasting just two or three years, before the long-term decline reasserted itself.

Even if all young Russian women could be persuaded to have several children, Mr Perevedentsev warns, the same is likely to happen again.

The seriousness of this problem has led to an urgent, polarised and often angry debate in Russia about ways to tackle the problem.

Many medical specialists berate the government's apparent inaction over the country's health crisis. It is estimated that a third of Russian men abuse alcohol, while smoking rates are among the highest in the world. New threats, such as the rapid spread of HIV/Aids, merely compound an already bad situation, they say.

Politicians on the nationalist wing of the political spectrum see the hand of the West, and of Russia's "enemies" more widely, in the population decline.

Ethnic rise

One commentary recently published by the "Rodina" (Motherland) movement suggested those Russian sociologists making the gloomiest predictions were, themselves, in the pay of western organisations committed, literally, to destroying Russia.

The population in regions such as Chechnya is growing

Meanwhile, Russian economists warn of the long-term consequences for the country's growth.

Some have suggested an official programme of controlled immigration, to encourage workers from the former Soviet republics and further afield to come to live and work in Russia. This is a controversial suggestion and appears to have been rejected at the very top.

In his recent state of the nation address, President Putin said "no sort of immigration will solve Russia's demographic problem".

At the same time, some officials and nationalist politicians have begun to utter a loaded term last used three decades ago by Soviet planners - "differentiated birth-rates".

Scare-mongering

It reflects concern that while ethnic Russians fare so badly, there are other, predominantly Muslim, population groups that are experiencing very rapid growth.

Some of the peoples of the North Caucasus - especially Chechens, Ingush and Dagestanis - are rapidly growing in number. The last Soviet census (1989), showed 611 Chechens for every 100,000 population. The most recent Russian census (2002) showed that figure had increased to 937 - an increase of more than 50%.

Mr Perevedentsev dismisses the notion that Russia could become a majority Muslim nation, and says this is a spectre being deliberately whipped up by politicians with little understanding of demography.

He acknowledges that there are very high birth-rates among these population groups, but insists they merely reflect an earlier stage of development and will ultimately fall. In 50 years' time, he says, Muslims will still be a small part of Russia's overall population.